The usual take on Elinor and Marianne is that Elinor is the reserved, rational one, and Marianne is the emotional, Romantic one. There is plenty of evidence in the book to support this interpretation, beginning with the initial description of the sisters in the first chapter: Elinor “possessed a strength of understanding, and coolness of judgment, which qualified her, though only nineteen, to be the counsellor of her mother,” while Marianne “was sensible and clever; but eager in everything: her sorrows, her joys, could have no moderation. She was generous, amiable, interesting: she was everything but prudent.”
But maybe the best way to understand this pair is to consider what they share, which is the problem of being a woman without property in Regency England, or, more specifically, the problem of being attached to men (Edward and Willoughby) who are false: Edward conceals his engagement to Lucy, and Willoughby, himself in want of money, drops the penniless Marianne to chase the heiress Sophia Grey. Their reactions are consistent with their personalities: when Lucy tells Elinor about her engagement, Elinor, though reeling, agrees to keep her secret. Marianne also is devastated by Willoughby’s cold behavior to her when they finally meet in London; in this case, her “understanding” with Willoughby is a secret that she is unable to keep (she falls into depression and mopes for days). Each sister, however, is bound by hopes that they dare not openly speak about; even Marianne, for all her lack of “prudence,” affirms to Elinor that she was never actually engaged to Willoughby, although “'I felt myself…to be as solemnly engaged to him, as if the strictest legal covenant had bound us to each other.’” In this sense one can understand the “sense/sensibility” dichotomy as different reactions to the same fundamental problem, which is the silence imposed on women. Neither Marianne or Elinor can give voice in any direct way to their desire, and it is their relationship to desire that shapes their personalities (cool or passionate, calculating or impulsive). It is a misreading, in my opinion, to see Elinor as the “smart” one or the one who comes out best; the point of the book instead is to show how each woman grows while trying to navigate the social relations that bind them.